This application claims priority to an application entitled, xe2x80x9cDevice and Method for Fabricating Diffractive Gratings,xe2x80x9d filed in the Korean Industrial Property Office on Jun. 29, 2000 and there duly assigned Serial No. 2000-36372.
1. Field of the Invention
The present invention relates generally to an apparatus and method for fabricating diffractive gratings, and particularly, to an apparatus and method for fabricating semiconductor material comprising gratings.
2. Description of the Related Art
Optical gratings have a variety of uses including frequency selection, optical feedback-type devices and wavelength dispersion. Easy, rapid, and reliable methods of making gratings of high quality with close spacing and high sensitivity are highly desirable in fabricating LDS.
Generally, diffractive gratings are fabricated using a photolithographic technique ordinarily used. A photoresist layer, which is resistant to the etching action, is first formed on a semiconductor substrate and irradiated by interference pattern light. After developing the phtotoresist, the semiconductor substrate is etched to a predetermined depth, except for the portion covered with the photoresist layer. Thereafter, the photoresist layer is removed from the substrate after etching.
FIG. 1 illustrates a conventional grating fabrication device 10, which includes a light source 11, a beam splitter 12, and reflective mirrors 13 and 14 for generating an interference pattern on a semiconductor material. The reflective mirrors 13 and 14 are arranged in such a way that the beams split by the beam splitter 12 can be focused on the surface of substrate 15.
The formation of diffractive gratings on a semiconductor substrate 15 using the conventional fabrication device 10 is explained hereinafter.
The surface of semiconductor substrate 15 is first cleaned, then a photoresist layer 16 about 500 Angstroms (xc3x85) thick or higher is formed on the semiconductor substrate 15. Then, the resultant structure is exposed to the light beams for a predetermined time. The interference pattern formed by the illumination of light is made by developing the photoresist. Here, the ratio of light exposed portions and unexposed portions covered with the photoresist layer 16 is about one-to-one. Interference pattern on the substrate is formed by etching with a predetermined solution (e.g., HBr-family etchant solution). Finally, the photoresist layer 16 is removed using a photoresist stropper, so that a pattern is obtained.
The conventional fabrication method, as described in the preceding paragraphs, has some drawbacks in that: (1) the manufacturing process is very complicated; (2) the frequent possibility of the thin photoresist layer 16 falling off the substrate 15 makes it difficult to achieve reproducibility and product yields; (3) the plasma ashing must be controlled by repeatedly measuring the light reflectance of the substrate 15 and continued until the intended light reflectance is achieved to form both the residual photoresist layer portions and the exposed portions at the intended ratio; (4) the measurement errors associated with the light reflectance measuring operation tend to diminish the accuracy; and, (5) the lengthy time (about 7 hours) associated in the fabrication process deteriorates the productivity and impedes the desired mass production.
It is, therefore, an object of the present invention to provide a device and process for fabricating diffractive gratings in a rapid and simplified way, thus increasing the product outputs as well as the product reproducibility.
To achieve the above object, there is provided a process for fabricating diffractive gratings which includes the steps of: providing a semiconductor substrate in a reactor, exposing an interference light pattern onto the semiconductor substrate; and, supplying a positive ion etchant solution in the reactor to etch the substrate via an oxidation-reduction process.
Preferably, the interference pattern exposurer device includes a light source, a beam splitter for splitting the light emitted from the light source into different paths, and light path changing means for focusing the split light beams at different angles onto the surface of the substrate.
Preferably, the reactor includes a support member for supporting the substrate, and the support member is selectively rotatable with respect to the reactor.
Preferably, interference patterns are formed on the substrate with different periods by changing the inclination of the substrate with respect to the incident light during the light irradiation step.